US3735325A

US3735325A - Rotary potentiometer with fine adjustment

Info

Publication number: US3735325A
Application number: US00252544A
Authority: US
Inventors: R Akashi
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-05-12
Filing date: 1972-05-12
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A miniature potentiometer of high accuracy comprises a support carrying an electrically resistive component extending about a support axis; a rotatable contact in wiping engagement with the component; a rotary member carried by the support to be rotatably adjusted; rotary gearing including sun, planet and ring gears to transmit rotation between the member and contact with mechanical advantage: and electrical terminals.

Description

United States Patent Akashi May 22, 1973 ROTARY POTENTIOMETER WITH FINE ADJUSTMENT 3,533,042 10/1970 Casey et al. ..338/162 Primary Examiner-Bernard A. Gilheany Assistant Examiner-D. A. Tone Attorney-William W. Haeflinger et al.

[5 7] ABSTRACT .A miniature potentiometer of high accuracy comprises a support carrying an electrically resistive component extending about a support axis; a rotatable contact in wiping engagement with the component; a rotary member carried by the support to be rotatably adjusted; rotary gearing including sun, planet and ring gears to transmit rotation between the member and contact with mechanical advantage: and electrical terminals.

7 Claims, 4 Drawing Figures ROTARY POTENTIOMETER WITH FINE ADJUSTMENT BACKGROUND OF THE INVENTION This invention relates generally to potentiometers, and more particularly concerns advances in the art of precision calibration adjustment of miniature potentiometers.

Modern circuitry compactness requires miniature components including potentiometers. Particularly is there need for highly accurate potentiometers of overall diameter less than about one-fourth inch. However, the demands of reduced size are in conflict with the requirements of high accuracy, since for example, reducing the length of the resistance component in a potentiometer normally results in diminished accuracy. Other requirements such as vibration and water proof construction are increasingly difficult to meet as the size of the potentiometer is reduced SUMMARY OF THE INVENTION It is a major object of the invention to provide a solution to the above requirements as well as others, the improved potentiometer characterized by unusual advantages, in construction, mode of operation and results. These include a design enabling increasing miniaturization without destroying accuracy; waterproof, dustproof and vibration proof construction; a gear trans mission that enables accurate adjustment; maximum resistor length and ease of fabrication of the resistor component; and consistent and dependable operation.

Basically, the potentiometer comprises a support means (as may include body and enveloping cover elements) defining a main axis and a resistance component extending about that axis (as for example with frusto-conical configuration); a rotatable electrical contact having wiping contact with the resistance component; a rotary adjustment member carried by the support means; rotary gearing connected to transfer rotary motion from the adjustment member to the contact and with mechanical advantage for calibration accuracy, as will be seen; and three electrical terminals respectively connected with the contact and spaced portions of the resistance component.

Typically, the gearing will include a sun gear connected with the adjustment member; planet gear means rotated by the sun gear and about fixed axes spaced from the main axis; and a ring gear arranged to be rotated about the main axis by the planet gear means, to rotate the contact at a substantially slower angular velocity than the angular velocity of the adjustment member. Further, the location and arrangement of these elements in relation to the remainder of the potentiometer enables extreme overall miniaturization, as will be seen.

Additional features include the carriage of the wiping contact by the ring gear at the side thereof opposite the planet and sun gear elements, and in such manner as to assure firm yieldable engagement of the contact with the resistance component in frusto-conical form for maximum length; and O-ring seals are located to benefit from compression in response to simple assembly of the cover into the body, as will be seen.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is an elevation taken in section through a potentiometer embodying the invention;

FIG. 2 is a horizontal section taken on lines 2-2 of FIG. 1;

FIG. 3 is a top plan view of the FIG. 1 potentiometer; and

FIG. 4 is a fragmentary plan view of the wiper contact seen in FIG. 1.

DETAILED DESCRIPTION In the drawings, the potentiometer 10 is seen to incorporate support means such as may include body and

cover elements

11 and 12. The body may consist of ceramic material, while the cover may consist of metal such as press steel, and may receive the body as shown, these elements defining a main axis 13.

An electrically resistive component is carried on the support means to extend arcuately about that axis; in particular, the resistive component may consist of a thin strip 14 (as for example silver base paint with resistive particles; as known) rolled into the frusto-conical body face 15 to itself define a frusto-conical arcuate surface 14a. The latter is engaged by a rotatable electrical contact 16 at the side of body 11 exerting pressure against the surface 14a, the contact consisting for example of beryllium copper. The contact also includes a fiat spring arm section 16a extending over the top of body 11, and bowed downwardly as shown to forcibly engage the conductive terminal plate 17 seated in a recess 18 in the top of body 11. Terminal pin 19 is solder connected to plate 17 and projects through and below the body to provide external electrical connection with confined wiper contact 16; and,

terminal pins

20 and 21 are connected by soldering with the arcuately spaced end portions of the resistive component 14, i.e., at

locations

20a and 21a, these pins also projecting below the body.

A rotary member 23 is carried by the support means to be rotatably adjusted, as by turning of a screw driver the tip of which fits in slot 24, in order to effect desired adjustment of the resistance characteristic of the potentiometer. The member 23 has successive sections 23a23d, as shown, section 23a received through an opening 25 through the cap or cover boss 12a, and section 23d seating on plate 17. Pressurally confined between flange section 23b and the cover is an elastomer O-ring 26 sealing off there between for dust and waterproof protection of the confined wiper contact and resistive component. Another O-ring 27 seals off between the lower skirt portion 28 of the cover and the body 11 to complete the dust free and water proof protection, and portion 28 is crimped inwardly during assembly to develop endwise force retaining the cap or cover on the body and pressurizing the O-ring 27.

In accordance with an important feature of the invention, rotary gearing is provided to be carried by the support means and connected to transmit rotation between the member 23 and the contact 16, and with mechanical advantage. As a result, turning of member 23 through a given angle results in rotary displacement of contact 16 through a substantially smaller angle, and typically less than one-fourth the given angle, producing greatly enhanced fine adjustment capability (or resistive calibration) of the potentiometer as compared with devices wherein adjustment and wiper elements are characteristically displaced through equal angles. Thus the member 23 may be revolved several times in order to displace the wiper contact through its complete range of engagement with the C-shaped resistance component 14.

In the example shown, the gearing includes a sun gear 30 on section 230 of member 23; planet gear means, as for example three planet gears 31 meshing with the sun gear and to be rotated about fixed axes 32 spaced from axis 13; and an internal ring gear 33 meshing with the planet gears and carried to be rotated about main axis 13 in response to planet gear rotation. The ring gear extends at 3311 beneath the planet gears to support same, the planet gears having annular configuration with cover offsets 34 received by the planet gears to locate them for rotation.

A guide slot 35 in the underside of ring gear section 33a receives the wiper contact bowed arm 16a, as shown. The construction is such that when the cover is assembled to the body, the arm 16a is yieldably urged against plate 17 for firm electrical contact, and also the contact 16 is yieldably and firmly urged inwardly against the resistive component 14, as described.

All gearing and the member 23 may advantageously consist of dielectric plastic material. Also, as seen in FIG. 2, body 11 may have a locating flat 50 at one side thereof.

Terminal pins

19, 20 and 21 may be staked in place at 51-53 on the body. Contact 16 may have a local V-shaped cross section adjacent component 15 as seen in FIG. 4, for rigidity and assurance of firm engagement with that component.

It should be noted that all moving parts as described are rotatable about axis 13, insuring accuracy and dependability of the potentiometer. Also, the resister 14 may alternatively comprise a copper wire rectangularly wound to form flat coils bonded to frusto-conical surface 15 of body 11, as for example by epoxide bonding agent.

I claim:

1. A potentiometer comprising a. support means defining a main axis and an electrically resistive component on said means and extending arcuately about said axis,

b. a rotatable electrical contact having Wiping engagement with said component,

c. a rotary member carried by the support means to be rotatably adjusted,

d. rotary gearing carried by the support means and connected to transmit rotation between said member and contact and with mechanical advantage,

' said gearing including a sun gear directly connected with said rotary member, planet gear means engaging the sun gear to be rotated about at least one fixed planet gear axis spaced from the main axis, and a ring gear carried by the support means to be rotated about the main axis by the planet gear means and to rotate the contact, and

e. three electrical terminals one of which is electrically connected with the contact, and the other two of which have electrical connection with arcuately spaced portions of said component.

2. The potentiometer of claim 1 wherein the contact includes a flat spring section carried by the ring gear and urged thereby to yieldably engage said component.

3. The potentiometer of claim 2 wherein the component has a frusto-conical outer surface engaged by the contact.

4. The potentiometer of claim 2 wherein the ring gear is grooved to receive the flat spring section in bowed configuration to yieldably engage a terminal plate on a body element, the ring gear rotating on a stem portion of the rotary member.

5. The potentiometer of claim 4 wherein the gear consists of dielectric plastic material; the body consists of ceramic, and the cover consists of metal.

6. The potentiometer of claim 1 wherein said support means includes body and cover elements, said component carried by the body and enveloped by the cover, and the cover carrying said gearing.

7. The potentiometer of claim 6 including O-rings sealing off between the body and cover and between the cover and said member, the cover defining an axial opening in which said member extends.

* i I! 1R

Claims

1. A potentiometer comprising a. support means defining a main axis and an electrically resistive component on said means and extending arcuately about said axis, b. a rotatable electrical contact having wiping engagement with said component, c. a rotary member carried by the support means to be rotatably adjusted, d. rotary gearing carried by the support means and connected to transmit rotation between said member and contact and with mechanical advantage, said gearing including a sun gear directly connected with said rotary member, planet gear means engaging the sun gear to be rotated about at least one fixed planet gear axis spaced from the main axis, and a ring gear carried by the support means to be rotated about the main axis by the planet gear means and to rotate the contact, and e. three electrical terminals one of which is electrically connected with the contact, and the other two of which have electrical connection with arcuately spaced portions of said component.